Microorganisms in the root canal system and their by-products cause pulpal and periapical inflammation (Kakehashi et al. 1965). Therefore incomplete disinfection of the root canal system is considered to be a major cause of persisting apical periodontitis (Seltzer & Bender 1967, Lin et al. 1992). Elimination of the microbial infection is one of the main goals of root canal treatment. Despite serious efforts, however, histologic and cultivation studies confirm the presence of persisting microorganisms after root canal treatment (Nair et al. 2005). One of the reasons of our inability to completely disinfect the root canal system is the complexity of its architecture (Vertucci 1984, Wu et al. 2000).
Another reason is that microorganisms like bacteria live in a bio film configuration (Costerton et al. 1995, Watnick & Kolter 2000). This makes them more resistant to endodontic treatment procedures. Thorough mechanical cleaning of the root canal system is impossible due to its complex morphology. Mechanical filing is performed to enable irrigation with antimicrobials. Current root canal irrigants have a superficial working range. The most potent disinfectant sodium hypochlorite does not penetrate lateral from the main canal due to its reactive nature. Inactivation occurs as soon as sodium hypochlorite encounters organic matter (Moorer & Wesselink 1982). Chlorhexidine does not penetrate into a biofilm (Zaura-Arite et al. 2001).
Irrigants like IKI (IPI), ethylalcohol or chlorhexidine are less effective in debriding the root canal system because they lack tissue dissolving properties.
On average 4 million CFU per tooth persist after chemo-mechanical debridement. Residual bacteria and other microorganisms that have access to the periapical tissues via accessory canals, sustain a chronic inflammatory process. Depending on the type of tooth, apical branching occurs in up to fifty percent of the teeth. Chronic infection and inflammation are responsible for failure of the endodontic therapy. Failure rates will increase with the introduction of CBCT (Cone Beam Computerized Tomography) due to the increase in detection of failure (Estrela et al. 2008). Root canal treatments are performed in two ways: i) one session in the dentist's chair, with NaOCl as disinfecting irrigant or ii) two or more sessions involving irrigation with NaOCl, while in between the sessions calcium hydroxide (Ca(OH)2) is enclosed in the root canal for further disinfection.
Ca(OH)2 is currently used as intracanal dressing in between two treatment sessions. With its pH of 12, Ca(OH)2 is weakly bactericidal. This is reported in several studies on bacterial suspensions (planktonic bacteria). In subjects diagnosed with apical periodontitis Ca(OH)2 is administered to reach additional disinfection and to prevent regrowth of the intracanal flora in between two treatment sessions.
Antimicrobial agents used in endodontics have certain disadvantages. For instance calcium hydroxide is only effective when it is in direct contact with the microorganisms (Siqueira & Lopes 1999). Furthermore, Ca(OH)2 is only bactericidal to some species, provoking a shift in the microbial flora towards more resistant species (Nakajo et al. 2006). Ca(OH)2 cannot eradicate E. faecalis, associated with failing endodontic treatments (Sirén et al. 1997, Sundqvist et al. 1998). Long term application of Ca(OH)2 weakens the dentine and remnants of the Ca(OH)2-paste are difficult to remove.
In our study interesting findings were observed. Dual-species bio films were exposed to Ca(OH)2. After an initial hundredfold bacterial reduction, the bacterial counts recuperated to a tenfold reduction after a week (end of experiment). This sheds doubts on the antibacterial efficacy of Ca(OH)2 on a biofilm. Furthermore the calcium hydroxide groups showed calcification of the biofilm in which the viable colonies harbored (Observation with confocal laser scanning microscopy after Dead/Live stain). The calcified plaque could not be removed from the model by swabbing with a cotton pellet or scraping with a hard plastic device. This was an interesting finding of the study because Ca(OH)2 is the only well accepted intracanal medicament in the world. If this calcification also occurs in the root canal, then this will hamper disinfection even more.
It is an objective of the present invention to provide improved disinfectant or antimicrobial compositions that can aid in overcoming the disadvantages of the treatments currently available.